1. Field of the Invention
This device relates to a speed-up valve and, in particular, it is concerned with a speed-up valve associated with a double-acting cylinder for the purpose of achieving an improved efficiency of operation by increasing the rod-extending speed of the double-acting cylinder.
Generally, it is sometimes desirable that one of the rod-extending motion and the rod-retracting motion of a double-acting cylinder is faster than the other. In case of an agricultural front loader, for example, it may be desirable that the dumping motion is faster than the scooping motion.
2. Description of the Prior Art
To this end, various proposals have been made: Increasing the size of hydraulic pumps and pipings; using a vacuum prevention valve to rapidly discharge the load under its own weight; and arranging a directional control valve in the form of a differential circuit. These proposals, however, have disadvantages in cost, operation and back-pressure rise involved due to pipings and valves used and have not been satisfactory.